The velocity-time graph of robber's car and a chasing police car are shown in the following graph. Police car crosses the robber's car in time

Options

A. 10 s after it starts
B. 1 s after it starts
C. 20 s after it starts
D. Never crosses

Answer

C

Explanation

From graph, velocity of robber's car `=10 ms^(-1)`
Let police car crosses it after t second.
Distance travelled by robber's car = 10 t m
Police car is moving with a constant acceleration of `1 ms^(-2)` as it attains a velocity of `10 ms^(-1)` in 10 s after starting from rest. Distance travelled in t second `=(1)/(2).a.t^(2)=(1)/(2)t^(2)`
When the police car crosses the arosses the robber's car, distance travelled by the both cars should be same from the starting point of chase.
`therefore (1)/(2)t^(2)=10t rArr t=20 s`